For many years, the most successful closure system for pharmaceutical products has been the use of rubber stoppers in glass or high-density plastic vials. The glass and rubber combination has been useful for a wide variety of pharmaceutical ingredients combining both safe storage of the medicines and easy access through the rubber stopper. Particularly when liquids are contained in the vial, a needle can easily penetrate the rubber stopper to withdraw the desired amount of ingredient without otherwise interfering with the completeness of the closure.
Because of the success of this type of pharmaceutical device, and as more and more systems started using rubber stoppers in glass containers, the rate at which these devices can be manufactured after filling the container contributes greatly to the economic efficiencies of the otherwise desirable design. Conventional pharmaceutical devices which are useful for filling vials rely upon a mechanical implantation of the rubber stopper into the neck of the vial or other shaped container. Just prior to the mechanical insertion, the rubber stoppers are transported from a hopper to the filling equipment, usually by centrifugal or gravity feed. It is essential that the rubber components not hang up on the transfer equipment but rather flow smoothly into the capping or closure forming device. The equipment especially for transferring components is normally made from stainless steel or other materials which can be kept extremely clean for pharmaceutical purposes.
In the prior art, the high coefficient of friction of rubber stoppers and other rubber materials which are being fed to closure devices and other pharmaceutical devices, has been the limiting factor in the speed of the machine. Use of gravity, centrifugal or vibration feeding devices require that the rubber stoppers or other elastomeric components move smoothly over the surface of the feeding unit. Typically, rubber devices of the type used in pharmaceutical closures have coefficients of friction of at least 1.2, which clearly acts as an impediment to rapid movement.
One solution which has been proposed to improve the general processibility of rubber closures and which has at least kept the individual rubber stoppers from bonding to one another during autoclaving and other treating steps is the use of silicone oil as a coating on the outside of the stoppers. Silicone oil has improved the lubricity of the rubber closures but has added additional problems by increasing the particle count found in inspection of various drug solutions. The Federal Drug Administration evaluates processes by counting the number of particles present, without concern for what the particles are made from. Silicone oil is normally not an undesirable particle in medicine but still adds to the count of particles and, therefore, detracts from the overall acceptance of its use in processing equipment. While the amount of silicone oil is minimal, only that amount necessary to prevent the individual stoppers from sticking to one another, it has not adequately affected the coefficient of friction of rubber stoppers for use in high-speed capping equipment so as to give uniform, faster movement, particularly with centrifugal feeding systems. Finally, the rubber stoppers which have been treated by the use of silicone oil are not as effective in surviving chemical tests concerning the compatibility and the contamination of the materials contained in the vials.
At the present time, there does not appear to be any suggestion in the prior art which would suggest the improvement of the coefficient of friction of rubber while maintaining other properties necessary for effective pharmaceutical closures. In U.S. Pat. No. 2,951,053, Reuter et al discusses an elastic polyurethane composition which has improved friction properties. The polyurethane is used to produce articles having moving surfaces, such as bearing designs and the like. Silicone oil and/or hydrocarbons are introduced into the polyurethane material. There is absolutely no suggestion that polyurethane may be used as a coating on the rubber products. U.S. Pat. No. 4,147,679 discloses a polyurethane which is suitable for forming a coating on substrates such as plastics, foam and the like. The use of polyurethane to solve the deficiencies outlined above in the use of elastomeric components in pharmaceutical devices has not been suggested by any of the prior art.